In an effort to understand the role of alterations in normal adhesive mechanisms in the carcinogenic process, we are employing immunochemical and immunocytochemical methods to identify and characterize macromolecules involved in adhesive interactions of normal and regenerating hepatocytes or primary and transplantable hepatocellular carcinomas (THC) induced in ACI rats by 2-acetylaminofluorene, ethionine, or diethylnitrosamine (DENA). Heteroantisera or monoclonal antibodies are being raised against intact hepatocytes, liver biomatrix, isolated plasma membranes, specialized intercellular junctions, or detergent solubilized components isolated on immobilized lectins. Reactivity of these antibodies with adhesive components is being assessed by examining the ability of Fab fragments to inhibit adhesive interactions. To date, we have identified a 105 kilodalton glycoprotein (designated Hep 105) which is expressed on the surface of both hepatocytes and bile duct epithelium and is tightly bound to liver biomatrix. We have shown that monoclonal antibodies specific for Hep 105 immunoprecipitate enzymatic activity associated with the enzyme dipeptidyl dipeptidase IV. We have further shown by immunofluorescence analysis of frozen sections that the expression of this glycoprotein is lost on primary hepatic tumors induced by DENA. In addition, we have produced monoclonal antibodies which recognize a 240 kilodalton protein of rat liver desmosomes. We have found that the expression of this demosomal antigen is lost or greatly reduced in all primary and transplantable hepatocellular carcinomas examined to date. Most recently, we have produced monoclonal antibodies against two 105 kilodalton glycoproteins involved in the intercellular adhesion of rat hepatocytes. These two glycoproteins have been shown to be very similar but not identical in structure. Further, we have demonstrated by immunoprecipitation analysis that these glycoproteins are either missing or expressed in a structurally altered form on 12/12 transplantable hepatocellular carcinomas, suggesting that the altered expression of this pair of cell adhesion molecules may be associated with the acquisition of the malignant phenotype. (A)